1. Field of the Invention
The present invention relates to display devices and driving methods thereof, and particularly to a display device using current-driven luminescence elements, and a driving method thereof.
2. Description of the Related Art
Conventionally, advancements in brightness, vividness, flatness, lightness, and increased surface area have been demanded of display devices, and technological development has also been progressing steadily. To satisfy the requirements of flatness, lightness, and increased surface area, liquid crystal displays and plasma displays have been introduced to the market, and continue to evolve even after more than ten years have passed since the start of commercialization.
In view of such an environment, recent years have seen the commercialization of displays using electroluminescence (referred to hereafter as EL) which allows luminescence intensity to be controlled according to the amount of current and which has an extremely fast response speed, and technological development has been progressing dramatically. In particular, organic EL displays using organic EL elements, which have excellent viewing angle characteristics, and are bright and vivid, have attracted attention as next-generation flat-panel displays having the advantage of low power consumption.
However, in the case of the above-mentioned current-driven organic EL display, brightness deterioration, which advances with the application of current to the organic EL elements, is particularly prominent. In order to restore organic EL elements affected by such brightness deterioration, a method of applying reverse bias voltage to the organic EL elements has been widely used, and Patent Reference 1 (Japanese Patent No. 3993117) discloses a circuit configuration for applying reverse bias voltage to EL elements.
FIG. 12 is a circuit diagram of a luminescence pixel in a conventional display device disclosed in Patent Reference 1. A display device 500 in the figure includes a luminescence element 501. FETs 502, 503, 504, and 505, a capacitance element 506, a data line 507, and control lines 508, 509, 510, and 511.
Signal voltage is supplied to the luminescence pixel from a data driver circuit not shown in the figure, via the data line 507. At this time, when the FET 503 is turned ON according to the voltage control from the control line 508, the signal voltage is applied to a gate of the FET 502, and a signal current corresponding to the signal voltage flows to the luminescence element 501 through the FET 502. Next, even when the FET 503 is turned OFF, the luminescence element 501 continues producing luminescence with a brightness corresponding to the voltage charged between both terminals of the capacitance element 506. In this manner, the basic display operation of the display device 500 is executed by the luminescence element 501, the FETs 502 and 503, the capacitance element 506, the data line 507, and the control line 508.
In addition to the above-described basic operation, in order to reverse the brightness deterioration in the luminescence element 501, a reverse bias voltage is applied to an anode of the luminescence element 501 while the signal current does not flow to the luminescence element 501. For example, when there is a short between both terminals of the capacitance element 506 according to the voltage control from the control line 509, the gate voltage of the FET 502 becomes Vss, and the FET 502 is turned OFF. During this period, the FET 505 is turned ON according to the voltage control from the control line 510. Measures to reverse the brightness deterioration in the luminescence element 501 are taken by applying a reverse bias voltage to the anode of the luminescence element 501, via the control line 511, at the same time as the FET 505 is turned ON.